Problems with the Dog

[John]

Hi Mark,

I've only seen the Pup with my 12" dob and it's position was to the east and very slightly to the south of Sirius A so, yes, to the right and it appeared to follow the much brighter star as it drifted across the field of view from west to east.

I believe a mak will show the same E-W orientation that the newt does but N will be at the top.

I find orthoscopics show the least amount of glare around the bright Sirus A and help allow the much fainter Pup star to be seen, often intermittently, glimmering though the diffraction "skirt" surrounding the very bright A star.

Hope you get it ! 

[Joves]

After reading and enjoying this thread, I decided to give it a go. One word sprung to mind more than once or twice whilst looking through the eyepiece (well, a few, but most were expletives)... IMPOSSIBLE!

What a challenge! Hats off several times to anybody who has been skillful/fortunate enough to see through the glare of Sirius A. I can't even say that I felt I was close to making it out, even with averted imagination. This has presented me with a personal challenge, for sure. Seems right up there with viewing the Horsehead visually to me!!

[AndyWB]

Well, I split Rigel last night pretty easily with the 130p, but there was no chance with Sirius - it was huge and blurry and rainbow coloured due to the atmosphere.

[Mark at Beaufort]

I know that using a Red filter has been mentioned before but I thought that this was an interesting read -

http://www.sydneyobservatory.com.au/2010/harry-sees-the-faint-companion-of-sirius-at-last-how-to-see-the-white-dwarf-sirius-b/

I currently do not have either a Red filter or an Orthoscopic EP. If I buy an Orthoscopic EP should it be for the Mak 180mm with its 2700 FL or my 10" Dob with its 1200 FL? Although I have Ethos EPs perhaps trying with my William Optics 12.5mm Planetary on the Mak 180mm might be a good starting point (216x) before spending more on additional EPs.

[Ouroboros]

I have a different problem with the dog. If I take him out with me star gazing he growls and barks at rustling hedgehogs and the like.

[alan potts]

Well still going down the road of not trying this above a UK latitude is rather taxing to say the least, the Dog star is being a bit of a pig. I started on it when it was at an elevation of 10 degree and of course it was like a welding arc almost requiring sun glasses, need I say had no hope of seeing anything. I allowed the star to drift to 16 degrees and thought this would sort of cover Manchester and above in the UK and again after 25 minute gave up, it must have been higher then and still nothing doing. The conditions were good but not excellent and the scope was my prefered 115mm APO with a slack handful of quality eyepieces.

As for scope size, Yes you could do it in a 5 inch but it is the conditions you need not the aperture.

Joves,    it would be nice to know how high in the sky it gets down there in Sydney, I am guess it is the wrong time of year for you to have this at best at a reasonable hour.

Alan.

[Joves]

Hi Alan,

It's currently sitting at zenith as we speak.

[Joves]

I've currently got the TV-76 pointed at it (ambitious, I know) with the 3mm Radian and it looks like it's having a fit before going supernova!

[Joves]

Considering the Pup is around mag 8, I'd probably be doing well to see it even if Sirius A wasn't in the picture!

[alan potts]

Arron,

Near the Zenith is about as good as you can get it but as you rightly said it's asking a lot of 76mm albeit a very high quality 3 inches. I have read reports of it being done with 70mm and I believe someone told me last year it has been done with 60mm over in America, I undertsand some parts have very low humidity with very clear skies, I don't think they were talking about LA. I have tried my 70mm without success so far as we get very dry air in January and February, though this year is awful, can you believe they are talking of water cuts, no rain or snow for 2 months.

I think you would have to pick your moment for conditions if you are any where near the City itself, you get a lot of heat rising from the buildings as you know.

Good luck ,

Alan.

[Joves]

I think you're right, Alan. My conditions are far from ideal. Plus, it's been a very warm, humid day today, so the atmosphere is bubbling.

I had moments where the seeing allowed a fairly tight image containing a handful of concentric rings surrounding the primary, but then it'd flare up again. I fitted my UHC filter to try contain it, which it did, but I'm pretty confident this stole enough photons to render the pup invisible.

Hmmm... It sure is a tricky one. Admittedly though, my experience with splitting doubles is pretty well zilch, so I probably should start on something a little less challenging. Fun though, I quite like the challenge.

[Mark at Beaufort]

I have been trying to work out the theoretical formula to establish the scope needed to split Sirius. This paper is very interesting -

http://www.jdso.org/volume4/number4/Napier_Munn.pdf

Taken from the article it states that 'very unequal pairs' have a Dawes limit of 914/D in mm. Therefore using my 180mm Mak that would mean 914/180 = 5 arc seconds. Thus looking at the current position of Sirius B in theory I should be able to see it. The only down side is sky darkness, transparency etc

Do you think that my theoretical judgement is correct?

[John]

The theory is fine Mark. It's when you actually try and do it the challenges start ! 

I've not managed to split it yet with my ED120 although I think it should be possible on a good night. I reckon I have been very close with that scope at times but that tiny spark of the Pup is really very elusive !!!

I'll just say again that orthoscopic eyepieces such as the Baader GO are noticeably better for this task than Radians, Ethos or the Pentax XW's. I have glimpsed it with these wider eyepieces but the ortho consistently makes the task that little bit easier.

[Mark at Beaufort]

I'll just say again that orthoscopic eyepieces such as the Baader GO are noticeably better for this task than Radians, Ethos or the Pentax XW's.

Thanks John for your advice it is much appreciated. Perhaps I could purchase the Baader 18mm Ortho Classic and using the bottom lens of the Baader barlow 1.3x  would give me a mag of 195x. The mag on the 10" Dob would need the complete Baader barlow 2.25x to produce 150x - but is this enough?

Alternatively I could get a more powerful EP getting less glass into the system. The 6mm Ortho in the Dob would give a mag of 200x.

[John]

Thanks John for your advice it is much appreciated. Perhaps I could purchase the Baader 18mm Ortho Classic and using the bottom lens of the Baader barlow 1.3x  would give me a mag of 195x. The mag on the 10" Dob would need the complete Baader barlow 2.25x to produce 150x - but is this enough?

Alternatively I could get a more powerful EP getting less glass into the system. The 6mm Ortho in the Dob would give a mag of 200x.

I have another idea Mark - I've sent you a PM 

[Joves]

John, do you think I'd have a better chance of splitting them with the LX90 or are the optics not likely to be up to the task?

[alan potts]

I don't see why a scope costing the amount they do should not be able to see it. They are surposed to have the same mirrors as the more costly LX 200 range in them though I have never had much luck with mine.

I am sure for you it is just case of getting it on the right night, I crack it when it is higher in my sky and when it is not absolutely dark, I managed it many times last year on lowish magnifications, however as it darkened it became more difficult. 

The method of only looking up to a point of degrees high in the sky is just my silly way of trying to understand what John and Mark and all the others are up against, I have to say they are doing a dam sight better job than I am. Having started this post I sort of though I would have delivered the goods by now but I am just red faced instead.

Alan.

[michael.h.f.wilkinson]

Maybe we are more used to lousy skies and have learned to deal with them (simply a matter of more practise). Having said that, I tried splitting Antares last summer from Tuscany, but failed rather dismally, due to horrendous seeing

[alan potts]

You may have something there Michael, we here have a high humidity at the moment with the odd day good. It is normal for us to have about 30% and a little more in Summer, it goes up when it rains and believe me that is not often enough, then it goes back down again. You all may well be more used to viewing in wet skies that as far as I can see make it more difficult to see detail, one night the Moon had no craters for a few seconds, what caused that Lord knows.

I am noticing a big difference so far this year in many areas of the hobby, doubles more difficult, less detail on planets and stars not as crisp as they were. I have checked all collimations and the eyepieces are the same more of less.

I am sure the Antatres affair was also to do with most of Italy being surrounded by water as well, I am lucky in as much I am 220 miles from the sea, this has to play a part in the seeing.

The only thing that seems different is the humidity this year.

Alan.

[michael.h.f.wilkinson]

Antares was also only visible directly over the roof of a house that had been baking in the summer sun all day. That did not help!

[chiltonstar]

You may have something there Michael, we here have a high humidity at the moment with the odd day good. It is normal for us to have about 30% and a little more in Summer, it goes up when it rains and believe me that is not often enough, then it goes back down again. You all may well be more used to viewing in wet skies that as far as I can see make it more difficult to see detail, one night the Moon had no craters for a few seconds, what caused that Lord knows.

I am noticing a big difference so far this year in many areas of the hobby, doubles more difficult, less detail on planets and stars not as crisp as they were. I have checked all collimations and the eyepieces are the same more of less.

I am sure the Antatres affair was also to do with most of Italy being surrounded by water as well, I am lucky in as much I am 220 miles from the sea, this has to play a part in the seeing.

The only thing that seems different is the humidity this year.

Alan.

...and yet here (Oxfordshire/Berkshire), I've had one or two nights of superb seeing (perfect, stable diffraction rings) when it's been particularly humid. In fact, it's been the humidity that has limited my observing times on those evening because of the fogging appearing all over all the optical surfaces (and I've learnt from bitter experience not to wave a hot air blower at optics - I just give up).

Chris

[John]

I have to be honest and say that I've never manged to get a really tight, airey disk on stars with any of the SCT's that I've owned. But it's a long time since I owned one .....

[alan potts]

I am not of the opinion they have changed very much John, the airy disc that is offered by both the 190mm M/N and the 115mm APO are better, I am not a big fan of them even though I have one,  I can't make my mind up about the 180mm Mak as i tend to only use it on limited targets. The little 150mm GSO RC was tight enough even though it is meant to be an astrograph, I think I will keep that after all.

Alan

[michael.h.f.wilkinson]

The Airy disc in an SCT can be pretty obvious, because due to the large central obstruction the first fringe of the diffraction pattern is much more pronounced. It is certainly not as tight as in a refractor or my old F/8 Newtonian. The diffraction disc can be reasonably stable, if seeing is OK.

[John]

One of the best non-refractors I've owned for a tight star image was the Intes 6" F/5.9 mak-newtonian. No secondary vanes and a tiny secondary make the views seem very much like a 5" apochromat refractor. I might consider a larger one of these in the future, as long as I can store it close to outside temperature.